Controllers are used throughout industry to control and monitor a wide range of machines and other movable components and systems. In an exemplary controller, such as that used in a PLC system, the controller may have power supply circuitry, I/O circuitry, interface circuitry, etc. combined with a processor, such as a CPU.
Generally, controllers are available with a wide range of capabilities and processing power. Conventional PLC systems utilize a plurality of modules that are mechanically mounted in a rack system and electrically connected along a back plane. The individual modules can be interchanged or replaced as required by a given system application.
Some PLCs, referred to as packaged controllers, typically are used for smaller machines or systems and include a single integral system having its own power supply, input/output circuitry, interface circuitry and processor in a single unit.
With packaged controllers, the entire controller e.g., PLC, must be purchased with appropriate power supply, I/O circuitry, interface circuitry, processor, etc. for the particular task or environment in which it will be used. The purchaser is limited to the available preconfigured controllers and has limited ability to upgrade a packaged controller system without purchasing a new system. Additionally, the purchaser is limited to the capabilities and features of the commercially available control systems.
It would be advantageous from both the customer's perspective and the manufacturer's perspective to design packaged controller assemblies having modular components that could be selectively interchanged. For example, it would be advantageous to have a PLC separated into two interchangeable components, such as a base unit containing a power supply, power supply circuitry, I/O circuitry, interface circuitry, etc., and a separate processor unit containing a control device, such as a CPU, for the base unit. Such a design would provide both the customer and the manufacturer great flexibility in delivering many configurations of a controller assembly with a smaller number of manufactured components.